Recently, the structure of the membrane glycoprotein (gp170) responsible for the active extrusion of foreign chemicals from certain drug resistant tumor cells (the so-called multidrug resistant phenotype; MDR) has been described in detail. The objective of this application is to test the possibility that this protein also participates in the secretion of certain chemicals by the kidney. The mammalian kidney plays a major role in the elimination of foreign chemicals, often via secretory processes such as the organic anion and organic cation systems. It is proposed to test the hypothesis that the gp170 (or a member of its gene family) is also responsible for the renal secretion of organic cations. Tissue and intracellular localization of the gp170 recently reported by others are consistent with the stated hypothesis. The proposed aims to test a functional role for the gp170 in renal organic cation secretion are: 1) To determine whether features of the renal organic cation secretory system are demonstrable in cells exhibiting the MDR phenotype; 2) To determine if antibodies to the gp170 inhibit the transport of organic cations by microvesicles isolated from renal brush border and basolateral membranes; 3) To determine whether the expression of the gp170 mRNA or levels of the gp170 protein coincide temporally with the postnatal development of the renal organic cation secretion system; and 4) To use the information gathered in specific aims 1 to 3 above to devise and implement a strategy to determine the primary structure (amino acid sequence) of the renal organic cation secretory protein. If the results support the hypothesis, the gp170 cDNA will be used to detect structural differences in the proteins from MDR cells and normal kidney. If the results fail to support the hypothesis, an alternative approach using monoclonal antibodies to select the cDNA for the organic cation carrier is proposed. The long-term goal is to define the structure of the renal secretory protein.